(noun) An area of featherless skin on a nesting bird’s breast, abdomen or sides that has thicker skin and a higher concentration of blood vessels in order to more efficiently transfer the parent bird’s body heat to the eggs that are being incubated. Many bird species develop brood patches, and either gender may develop one depending on whether or not the incubation duties are shared.
In many bird species, the feathers around the brood patch fall out naturally during nesting season, though some species, such as many ducks, will intentionally pluck the feathers and use them to line the nest for better heat retention around the eggs. The exact size and location of the brood patch varies for each bird species, and the feathers will regrow shortly after the eggs have hatched. In altricial bird species such as songbirds, it may take slightly longer for the feathers to return since the helpless hatchlings will need their parents’ help to regulate body temperature until they have grown their own feathers.